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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here! |
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02-23-2019, 07:40 AM | #46 |
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Re: Rollergun Recoil and the Jerk (not the owner!)
Because some of them have a shock absorber in the band drive (roller band wrappers) and some have a hydrodynamic brake in the moving side pulleys, and also because the gun has more weight with the axle and rollers, there ain't no magic involved.
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02-23-2019, 08:00 AM | #47 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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And what is wrong with that....the thread is about rollers and the lack of recoil. Fact is rollerguns shoot larger shafts in smaller guns very successfully. Where no small banded speargun can do the same. Forgetting about mechanical effectiveness for a moment I can say that after using smaller inverted rollers spearfishing efficiency is increased dramtically with smaller inverted rollers. |
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02-23-2019, 08:08 AM | #48 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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03-19-2019, 12:07 AM | #49 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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03-19-2019, 01:06 AM | #50 |
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Re: Rollergun Recoil and the Jerk (not the owner!)
Before Seal passed away he had been showing that very high velocities were possible with thinner shafts using Rollerguns. The idea that a Shaft diameter has a terminal velocity may not be correct. With a progressive powering like a Roller gun, and a stable platform, even thinner shafts may be stable at very high velocities like 30+mtr/sec?
We really lost one of the great ones with him. I miss you SEAL.
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03-19-2019, 01:27 AM | #51 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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OK, I found it, I was having some health issues myself and in early 2018 through to well past mid year I sort of disappeared myself and never used my computer for most of 2018, being in hospital for a month or more with things looking grim. That is how I missed it. http://www.spearboard.com/showthread...ighlight=kosta Last edited by popgun pete; 03-19-2019 at 01:45 AM. |
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03-19-2019, 07:59 AM | #52 |
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Re: Rollergun Recoil and the Jerk (not the owner!)
It's been a bit more than a year since Seal's passing and the circumstances and the tragedy have certainly been in the back of my head as I have spent the last month diving in the same part of the world as he last did. I think I am more aware of the dangers because of Jon's thread - and I also got myself an FRV, in part sparked by Kosta's accident.
But back to rollerguns... It is often mentioned that they shoot "progressively", but can someone please once and for all explain to me how that is? Or is it myth? Why would rubbers all of a sudden change their dynamics just because they are on the bottom;-)? Or is it because a pre-stretched roller operates at higher stretch and/or in a range of its stretch that is more progressive? I feel like at least some of the rollers can not be said to be progressive but I might be missing something. Last edited by Diving Gecko; 03-19-2019 at 12:34 PM. |
03-19-2019, 12:43 PM | #53 |
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Re: Rollergun Recoil and the Jerk (not the owner!)
How the overpowered enclosed track speargun shoot accurate ?if the gun move the spear also move , enclosed track holding the spear till it leave the muzzle ,I build one and i couldn't shoot accurately with 7mm spear ,also once the rubber exit the roller holes and wishbone hit the bridge there is a shock hit not sure if it affect the spear travelling in heavy set up ,
one more question the bridge width should be wider enough to avoid impact of shark fin and changing the spear direction ,this in case of the spear rotate or it doesn't have any effect?,I have used 15 mm internal width and it work great but the sigal sub have very narrow piece as in pictures . |
03-19-2019, 12:53 PM | #54 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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If you look at the diagrams here then you can see rollerguns can seem more powerful than they are if all guns are using the same band stretch. In Rollergun 10 a three band gun has more energy than a twin axle band wrapping rollergun using the same band stretch and that is before subtracting the losses in energy going around the rollers. Another way to look at is to imagine a standard band gun with rollers just back from the muzzle where the bands do a wrap around the rollers for a full 360 degrees and then proceed to the rear of the gun. These rollers have wide flanges to allow the double width and they are going to do nothing but absorb energy. So a shot from this gun is going to be less powerful than from the same gun with these parasitic rollers removed. By the way there is a gun patent for this system, but the fact that there are no such guns speaks for itself. Last edited by popgun pete; 03-19-2019 at 04:05 PM. |
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03-19-2019, 01:09 PM | #55 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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Although difficult to check there will also be blue marks left inside the enclosed track. If the track was fully enclosed then the shaft would skate on a squeeze film between it and the barrel wall and the frictional drag is much less. Pneumatic guns avoid these problems by shooting an 8 mm spear out of a 13 mm diameter inner barrel, so there is 2.5 mm clearance on the side of the shaft to the inner barrel wall, but the shaft is held firmly by the piston at its tail and the centralizing washer/stop ring sitting in the muzzle entrance. On band guns with line slides the spear can similarly be constrained by a stop ring sitting in the muzzle, but the spear tail is not confined by anything other than the wishbones. If you look at the Ocean Rhino and the prior Spearfishing Specialities spearguns they use a long confining muzzle to "iron out" the spear as well as a centralizing washer in the muzzle. Last edited by popgun pete; 03-19-2019 at 01:28 PM. |
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03-19-2019, 01:44 PM | #56 |
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Re: Rollergun Recoil and the Jerk (not the owner!)
Although bands are more powerful these days than in the past you only have to look at the Sampson Gun from the sixties, early seventies to see a different philosophy at work. That gun used a 3/8" shaft, which was pretty heavy duty so not likely to bend, a heavy duty line slide confined in the muzzle and a great big gap between the spear and the barrel tube. The reason for the latter was the spear was not going to hit the barrel no matter how much it bent. The problem with the Sampson Gun was it had a poor trigger mechanism which moved the spear backwards against the band pull when you squeezed the trigger. So strong trigger fingers were required. How do I know this? Well my Sampson Gun leans in the corner of the room where I am typing this up and the only way to describe it is a eurogun on steroids. I should add that it is a Short Tom and not a Long Tom, which was out of my league, and only used by big guys who had the reach and strength to load it.
Last edited by popgun pete; 03-19-2019 at 01:53 PM. |
03-19-2019, 01:50 PM | #57 |
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Re: Rollergun Recoil and the Jerk (not the owner!)
Doyen of Castle, I'm not sure the long Bridge 6" before your rollers is doing you any favors. That looks like it would cause a disturbance before your shaft left the gun.
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03-19-2019, 02:18 PM | #58 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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P.S. Fastest piston engine propeller driven fighter-bomber of WWII, only twenty or so built, this is the only one left and after storage for decades at the Silver Hill facility was sent back to Germany where Dornier completely rebuilt it, now at the Smithsonian National Air and Space Museum https://airandspace.si.edu/collectio...-0-pfeil-arrow Last edited by popgun pete; 03-19-2019 at 04:26 PM. |
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03-19-2019, 05:41 PM | #59 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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The idea of rollers came up brilliantly simple: to give a much greater band lenght by turning the bands over through rollers. What this gives is the following: It translates to a longer bands, which when contracting loose the power over time slower since the band power is only determined by its stretch ratio. This results in bigger band stretch/gun lenght ratio. This actually means that when the rubber traverses the same amount of path when pushing the shaft it lost less of its pulling power, since its stretch ratio reduced less because the gun is longer. To top it off, the rubber is pre-stretched which also increases the band power/time curve. The losses that occur at the turning is negligible compared to the benefits in the process. And thats all there is. What demultiplied guns did, is similar to the standard rollers, although even better. They took advantage that since the distance that the cable travels (that is pulling the shaft) is double that of the rubber. This means that our power/time curve is better since the rubber looses energy slower compared to non-demultiplied systems. It does have the disadvantage that power of each rubber in the demultiplied system is divided by its demultiplication factor. It can be compensated by adding extra rubber on the bottom side, but not only this, its also partly compensated by the fact that once you start rigging the gun (pulling the rubber, or in this case the cable first) your first stroke can be adjusted power-wise that its the same as the non-reduced. This is achieved by using the thicker rubber at bigger stretch ratios, or by pulling more then one rubber at once. This effectively means that, our first cable pull equals to same amount of power on the cable as any other classic rubber gun, except that the power is lost slower along the pull path. The energy losses in such system because of "extra moving parts" are also negligible since, mechanically speaking each movement through the water can be seen as a waste. With that in mind, i think that we can agree that the cable has less energy losses than the rubber, and that the pulley systems have less energy losses because they travel only half the distance compared to the cable or classic bands. They also don't need to accelerate as fast, since the cable traverses at double their speed.
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03-19-2019, 05:50 PM | #60 | |
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Re: Rollergun Recoil and the Jerk (not the owner!)
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